Show HN: We made a small and cheap network switch

Original Article ↗ Hacker News Discussion ↗

Use Case & Hardware Design

  • Designed primarily for an underwater robot; priorities are low cost, very small footprint, and integration into existing 12 V / 3.3 V systems.
  • 5‑port, 10/100 Mbps unmanaged switch using Molex Picoblade connectors instead of RJ45 to minimize size; cable is spliced from standard Ethernet.
  • Magnetics are implemented on the board (“external to the chip, integrated on PCB”), allowing very compact “ports.”
  • Layout and schematics are open source; boards designed in KiCad (nightly) and viewable via kicanvas.

Performance & Feature Set

  • 100 Mbps Fast Ethernet was chosen because the robot’s tether bandwidth is the bottleneck and higher speeds would add cost, pins, and board area.
  • 100 Mbps is defended as still common and appropriate in embedded and industrial contexts.
  • The switch IC supports VLANs, QoS, LACP, mirroring, etc., but these require an EEPROM that was removed in V2 to save cost and space; V1 supported them.
  • Line‑rate switching is believed but not rigorously characterized; throughput tested at 100 Mbps with iperf.
  • Auto‑MDIX behavior is unclear; team hasn’t fully characterized it.

Cost, Size & Market Positioning

  • Claimed BOM is around $4–5; small production run cost about $7 per assembled board. Others argue BOM “in reality” is whatever you pay at your volume.
  • Commodity 10/100 and even gigabit desktop switches with cases and PSUs can be had for $7–10, so cost leadership is disputed.
  • Size leadership is refined: positioned as “world’s smallest 5‑port unmanaged switch,” noting smaller 3‑port commercial modules exist.
  • Several comments stress that desktop switches are not suitable for robotics or tightly constrained embedded spaces; this board targets that niche and the open‑hardware community.

Power & Thermal Considerations

  • On‑board LDO stepping down from up to 12 V to 3.3 V runs hot (~60°C) at load; heatsinking and thermal vias are used, and an upstream buck is recommended in practice.
  • Some suggest moving to a buck converter or shared 5 V rail for efficiency, while others note LDOs’ simplicity and low noise.

Open Source, Tools & Learning

  • Full design files are published; team emphasizes democratizing hardware and showing that advanced boards can be built without formal degrees.
  • Discussion branches into PCB tools, simulation/DFM (e.g., Quilter), and general learning resources.
  • Multiple commenters praise the educational value, expressed interest in buying boards, and suggest selling via hobbyist platforms.